By Christian Elliott and Brittany Edelmann
Nearly 20 years ago, then Ph.D. student Gina Moseley walked into a bar in Bristol to meet fellow members of the University of Bristol Spelæological Society caving club. An older caver talked with her over drinks about some small caves in northeastern Greenland he’d always dreamed of organizing an expedition to explore. But, “logistically, it’s a nightmare to get out there,” said Moseley, now a professor in the Institute of Geology at the University of Innsbruck in Austria. The caver gave her all the papers he’d collected on the caves, and for years she kept them filed away.
Much later, a 1960 article by U.S. military geologists among the papers caught her eye. In their search for prime airfield locations, the geologists discovered caves with interesting geological features — crystalline calcite, stalagmites and flowstone deposits. To Moseley, that was proof Greenland’s caves contained something critical to scientists’ understanding of Earth’s ancient climate.
Moseley took her first steps into caving years earlier with her mom on a holiday trip when she was 12. She loved it. As she started grad school in Bristol, she discovered she could bring together her fascination with caves and her interest in studying paleoclimate to understand how future climate change — pushed by fossil fuel emissions of human activities — will affect the Earth.
Caves are normally “not altered or impacted by other processes” and “they’re so well-preserved over thousands of years,” Moseley said. That makes them a great location for climate research and creating records that can function as important analogs for future climate change.
The 2021 Comer Climate Conference on Oct. 4 – 5 brought together scientists from around the world, including Moseley and fellow paleoclimate researcher Kathleen Wendt.
“Devil’s Hole was where it all began. That was the start of cave paleoclimate research,” Moseley said. Paleoclimate scientists first rappelled down into the deep, narrow cave in the Amargosa Desert in southwest Nevada in the late 1980s.
Using cores of the thick calcite crusts on the cave walls, which accumulated steadily over time, researchers reconstructed 500,000 years of climate history here with Uranium-thorium dating. Uranium-thorium dating provides insight into when a rock was formed– giving a date to the origin of the rock.
Devil’s Hole was also where Moseley and Wendt, who has her Ph.D. from the University of Innsbruck in Austria, got their start in cave paleoclimate science. In 2017, they returned to Devils Hole to extend the climate record further and validate the older results.
In their research Moseley and Wendt focused on oxygen isotopes, which provide temperature information about historic temperatures. During ice ages, a heavier isotope of oxygen forms at higher levels than during warm spells.
Wendt is getting ready to submit a new paper on the oxygen isotope record from Devils Hole. By showing the fluctuation in types of isotopes, heavier versus lighter forms of oxygen, this will give “clues into changes in temperature and a little bit about the source of precipitation over time,” Wendt said.
They found the water table dropped below modern levels during the last interglacial, 120,000 years ago, when Earth’s orbit brought the planet closer to the sun. That time period is an analog for southern Nevada’s hotter and drier future that will be accelerated beyond natural planetary fluctuations with human-forced extremes of climate change.
“Studying the paleoclimate tells us what nature is capable of,” Wendt said.
The Greenland caves
Paleoclimatologists who focus on caves often study speleothems — mineral deposits formed by dripping water. Protected within caves from the elements, these dripstones (stalagmites and stalactites) and flowstones grow as layers of calcium carbonate carried by rainwater add up over hundreds of thousands of years.
One of the flowstones Moseley found in the caves was specifically mentioned in the 1960 paper that inspired the expedition.
In Greenland, now a rainless polar desert, speleothems formed during a time when the island’s climate was warmer and wetter. By collecting and sampling speleothems, Moseley can reconstruct that ancient climate period as an analog for the future, when Greenland will once again be warmer and wetter.
Over millions of years due to orbital changes, Earth’s climate alternates between warm and cold periods — interglacials and ice ages called glacials. Paleoclimatologists rely on air bubbles in cores taken from ice sheets in Greenland and the Antarctic to study the composition of the ancient climate’s atmosphere, but there’s a problem — during warm periods, the ice sheet melts. That’s where the caves come in.
“So the caves offer the polar opposite of what the ice cores do because the ice cores tend to be cold-based climate records and the caves can give us warm-based climate records. So, we get to the two different parts together,” Moseley said.
That’s a common theme in paleoclimatology — no one climate proxy shows the big picture. To fully understand Earth’s ancient climate, scientists must piece together hundreds of pieces from data from sources across the world.
“If you have one cave in one location, that’s kind of interesting. But if you can relate that to other caves in other locations, ice cores in other locations, deep sea sediments in other locations and get the whole picture, that’s where it really gets interesting. That’s where we can answer the big questions and tackle the big issues,” Moseley said.
As the Arctic continues to warm at twice the rate of the rest of the world, understanding what warm and wet historic climate periods were like can help scientists know what to expert in the imminent future.
This leads to Moseley’s next adventure in 2023, where she will explore completely untouched caves in Northern Greenland. This was only made possible with an award from Rolex — which provides funding for such an endeavor.